Organic light-emitting diode display having high aperture ratio and method for manufacturing the same

ABSTRACT

An organic light-emitting diode display can include a substrate in which an emission area and a non-emission area are defined; a first transparent conductive layer, a light shielding layer, a buffer layer and a semiconductor layer sequentially laminated on the non-emission area; a gate electrode superposed on the center region of the semiconductor layer, having a gate insulating layer interposed therebetween; a drain electrode coming into contact with one side of the semiconductor layer, having an interlevel insulating layer covering the gate electrode interposed therebetween, and formed of a second transparent conductive layer and a metal layer laminated thereon; a first storage capacitor electrode disposed under the interlevel insulating layer in the emission area and formed of the first transparent conductive layer; and a second storage capacitor electrode superposed on the first storage capacitor electrode, having the interlevel insulating layer interposed therebetween, and formed of the second transparent conductive layer.

This application claims the priority benefit of Korean PatentApplication No. 10-2014-0158322 filed on Nov. 13, 2014, which isincorporated herein by reference for all purposes as if fully set forthherein.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an organic light-emitting diode displayhaving an aperture ratio improved by forming a storage capacitor in anemission area using a transparent conductive material, and to a methodfor manufacturing the same. In addition, the present invention relatesto an organic light-emitting diode display and a method formanufacturing the same for simplifying a manufacturing process byreducing the number of mask processes.

Discussion of the Related Art

Recently, a variety of flat panel displays having reduced weight andvolume, compared to cathode ray tubes, has been developed. Such flatpanel displays include liquid crystal displays (LCDs), field emissiondisplays (FEDs), plasma display panels (PDPs), electroluminescentdevices (ELs) and the like.

ELs are classified into an inorganic EL and an organic light-emittingdiode display and are self-emissive devices having the advantages ofhigh response speed, luminous efficiency and brightness and wide viewingangle.

FIG. 1 illustrates a structure of an organic light-emitting diodeaccording to the related art. As show in FIG. 1, the organiclight-emitting diode includes an organic electroluminescent compoundlayer, a cathode and an anode opposite to each other and having theorganic electroluminescent compound layer interposed therebetween. Theorganic electroluminescent compound layer includes a hole injectionlayer (HIL), a hole transport layer (HTL), an emission layer (EML), anelectron transport layer (ETL) and an electron injection layer (EIL).

The organic light-emitting diode emits light according to energy fromexcitons generated through a process in which holes and electronsinjected to form the anode and the cathode are recombined in the EML. Anorganic light-emitting diode display displays images by electricallycontrolling the quantity of light generated in the EML of the organiclight-emitting diode as shown in FIG. 1.

Organic light-emitting diode displays (OLEDDs) using the characteristicsof the organic light-emitting diode which is an electroluminescentdevice are classified into a passive matrix type organic light-emittingdiode display (PMOLED) and an active matrix type organic light-emittingdiode display (AMOLED).

The AMOLED displays images by controlling current flowing throughorganic light-emitting diodes using a thin film transistor (referred toas TFT hereinafter).

FIG. 2 is an equivalent circuit diagram illustrating a structure of onepixel of an organic light-emitting diode display according to therelated art, FIG. 3 is a plan view of the structure of one pixel of theorganic light-emitting diode display according to the related art andFIG. 4 is a cross-sectional view illustrating the structure of theconventional organic light-emitting diode display, taken along line I-I′of FIG. 3.

Referring to FIGS. 2 and 3, an AMOLED includes a switching TFT (TFT) ST,a driving TFT DT connected to the switching TFT ST and an organiclight-emitting diode OLED in contact with the driving TFT DT.

The switching TFT ST is formed at an intersection of a scan line SL anda data line DL and serves to select a pixel. The switching TFT STincludes a gate electrode SG, a semiconductor layer SA, a sourceelectrode SS and a drain electrode SD. The driving TFT DT drives anorganic light-emitting diode OLED of a pixel selected by the switchingTFT ST. The driving TFT DT includes a gate electrode DG connected to thedrain electrode SD of the switching TFT ST, a semiconductor layer DA, asource electrode DS connected to a driving current line VDD and a drainelectrode DD. The drain electrode DD of the driving TFT DT is connectedto an anode ANO of the organic light-emitting diode OLED.

More specifically, referring to FIG. 4, the gate electrodes SG and DG ofthe switching TFT ST and the driving TFT DT are formed on a substrateSUB of the AMOLED. A gate insulating layer GI is formed on the gateelectrodes SG and DG. The semiconductor layers SA and DA are formed onportions of the gate insulating layer GI, which correspond to the gateelectrodes SG and DG. The source electrode SS and the drain electrode SDare formed on the semiconductor layer SA, opposite to each other havinga predetermined gap provided therebetween. The source electrode DS andthe drain electrode DD are formed on the semiconductor layer DA,opposite to each other having a predetermined gap provided therebetween.The drain electrode SD of the switching TFT ST is connected to the gateelectrode DG of the driving TFT DT via a contact hole formed in the gateinsulating layer GI. A passivation layer PAS is formed on the overallsurface of the substrate so as to cover the switching TFT ST and thedriving TFT DT having the aforementioned structure.

When the semiconductor layers SA and DA are formed of an oxidesemiconductor material, a high resolution and fast driving speed can beachieved in a large TFT substrate having large charging capacity due tothe oxide semiconductor's high mobility. The oxide semiconductormaterial layers may further include etch stoppers SE and DE forprotecting the surfaces thereof from an etchant in order to ensuredevice stability. Specifically, the etch stoppers SE and DE are formedso as to prevent the semiconductor layers SA and DA from beingback-etched due to an etchant contacting the exposed surfaces of thesemiconductor layers SA and DA, which correspond to the gaps between thesource electrodes SS and DS and the drain electrodes SD and DD.

A color filter CF is formed in a region corresponding to the anode ANOwhich will be formed later. The color filter CF is preferably formed tooccupy a wide area if possible. For example, the color filter CF isformed such that the color filter CF is superposed on a wide areaincluding the data line DL, driving current line VDD and scan line SL.The substrate on which the color filter CF has been formed has an unevensurface and many stepped portions since a lot of components have beenformed thereon. Accordingly, an overcoat layer OC is formed on theoverall surface of the substrate in order to planarize the surface ofthe substrate.

Subsequently, the anode ANO of the OLED is formed on the overcoat layerOC. Here, the anode ANO is connected to the drain electrode DD of thedriving TFT DT via a contact hole formed in the overcoat layer OC andthe passivation layer PAS.

A bank pattern BN for defining a pixel region is formed on the switchingTFT ST, the driving TFT DT and the interconnection lines DL, SL and VDDformed on the substrate on which the anode ANO is formed.

The anode ANO exposed through the bank pattern BN becomes an emissionarea. An organic emission layer OLE and a cathode layer CAT aresequentially formed on the anode ANO exposed through the bank patternBN. When the organic emission layer OLE is formed of an organic materialemitting white light, the organic emission layer OLE expresses a colorassigned to each pixel according to the color filter CF located underthe organic emission layer OLE. The organic light-emitting diode displayhaving the structure as shown in FIG. 4 is a bottom emission displaywhich emits light downwardly.

In such a bottom emission organic light-emitting diode display, astorage capacitor STG is formed in a space in which the anode ANO issuperposed on the gate electrode DG of the driving TFT DT. The organiclight-emitting diode display displays image information by drivingorganic light-emitting diodes. Here, a considerably large amount ofenergy is necessary to drive the organic light-emitting diodes.Accordingly, a large-capacity storage capacitor is needed in order tocorrectly display image information having rapidly changing data values,such as video.

To secure a storage capacitor having sufficient capacity, a storagecapacitor electrode needs to have a sufficiently large area. In thebottom emission organic light-emitting diode display, a light emittingarea, that is, an aperture ratio, decreases as the storage capacitorarea increases. In a top emission organic light-emitting diode display,the storage capacitor can be formed under the emission area and thus theaperture ratio does not decrease even when a large-area storagecapacitor is designed. However, the area of the storage capacitor isdirectly related to aperture ratio decrease in the bottom emissionorganic light-emitting diode display.

To manufacture such an organic light-emitting diode display, aphotolithography process using a photo-mask is performed multiple times.Each mask process includes cleaning, exposure, development, etching andthe like. When the number of mask processes increases, time and costsfor manufacturing the organic light-emitting diode display and a defectgeneration rate increase, decreasing production yield. Accordingly, itis necessary to reduce the number of mask processes in order to decreasemanufacturing costs and improve production yield and productionefficiency.

SUMMARY OF THE INVENTION

To solve the aforementioned problems and other limitations associatedwith the related art, the present invention provides an organiclight-emitting diode display and a method for manufacturing the same forsecuring a storage capacitor having sufficient capacity withoutdecreasing an aperture ratio by forming the storage capacitor in anemission area using a transparent storage capacitor electrode. Anotherobject of the present invention is to provide an organic light-emittingdiode display and a method for manufacturing the same for simplifying amanufacturing process by reducing the number of mask processes.

In one aspect, an organic light-emitting diode display includes asubstrate in which an emission area and a non-emission area are defined;a first transparent conductive layer, a light shielding layer, a bufferlayer and a semiconductor layer sequentially laminated on thenon-emission area; a gate electrode superposed on the center region ofthe semiconductor layer, having a gate insulating layer interposedtherebetween; a drain electrode coming into contact with one side of thesemiconductor layer, having an interlevel insulating layer covering thegate electrode interposed therebetween, and formed of a secondtransparent conductive layer and a metal layer laminated thereon; afirst storage capacitor electrode disposed under the interlevelinsulating layer in the emission area and formed of the firsttransparent conductive layer; and a second storage capacitor electrodesuperposed on the first storage capacitor electrode, having theinterlevel insulating layer interposed therebetween, and formed of thesecond transparent conductive layer.

In another aspect, a method for manufacturing an organic light-emittingdiode display includes forming a first transparent conductive layer, alight shielding layer, a buffer layer and a semiconductor layer on anon-emission area of a substrate using a first transparent conductivematerial, a light shielding material, an insulating material and asemiconductor material, respectively, and forming a first storagecapacitor electrode on an emission area of the substrate using the firsttransparent conductive material; forming a gate electrode superposed onthe center region of the semiconductor layer, having a gate insulatinglayer interposed therebetween; forming an interlevel insulating layer onthe overall surface of the substrate on which the gate electrode isformed; and forming, on the interlevel insulating layer, a drainelectrode coming into contact with one side of the semiconductor layerand formed of a second transparent conductive layer and a metal layerlaminated thereon, a source electrode coming into contact with the otherside of the semiconductor layer and formed of the second transparentconductive layer and the metal layer laminated thereon, and a secondstorage capacitor electrode superposed on the first storage capacitorelectrode and formed of the second transparent conductive layer of thedrain electrode, extended to the emission area.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 illustrates an organic light-emitting diode display according tothe related art:

FIG. 2 is an equivalent circuit diagram illustrating a structure of onepixel of the organic light-emitting diode display according to therelated art;

FIG. 3 is a plan view illustrating the structure of one pixel of theorganic light-emitting diode display according to the related art;

FIG. 4 is a cross-sectional view illustrating the structure of one pixelof the conventional organic light-emitting diode display, taken alongline I-I′ of FIG. 3;

FIG. 5 is a plan view illustrating a structure of an organiclight-emitting diode display according to a first embodiment of thepresent invention;

FIG. 6 is a cross-sectional view illustrating the structure of theorganic light-emitting diode display according to the first embodimentof the present invention, taken along line II-II′ of FIG. 5;

FIGS. 7A to 7J are cross-sectional views illustrating a method formanufacturing the organic light-emitting diode display according to thefirst embodiment of the present invention;

FIG. 8 is a plan view illustrating a structure of an organiclight-emitting diode display according to a second embodiment of thepresent invention;

FIG. 9 is a cross-sectional view illustrating the structure of theorganic light-emitting diode display according to the second embodimentof the present invention, taken along line III-III′ of FIG. 8; and

FIGS. 10A to 10J are cross-sectional views illustrating a method formanufacturing the organic light-emitting diode display according to thesecond embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to embodiments of the invention,examples of which are illustrated in the accompanying drawings. Whereverpossible, the same reference numbers will be used throughout thedrawings to refer to the same or like parts. It will be paid attentionthat detailed description of known arts will be omitted if it isdetermined that the arts can mislead the embodiments of the invention.

First Embodiment

A description will be given of an organic light-emitting diode displayaccording to a first embodiment of the present invention with referenceto FIGS. 5 and 6. FIG. 5 is a plan view illustrating a structure of anorganic light-emitting diode display according to the first embodimentof the present invention and FIG. 6 is a cross-sectional viewillustrating the structure of the organic light-emitting diode displayaccording to the first embodiment of the present invention, taken alongline II-II′ of FIG. 5. All the components of the organic light-emittingdiode display according to this embodiment and all other embodiments areoperatively coupled and configured.

Referring to FIGS. 5 and 6, the organic light-emitting diode displayaccording to the first embodiment of the present invention includes asubstrate SUB in which an emission area AA and a non-emission area NAare defined, a switching TFT ST, a driving TFT DT connected to theswitching TFT ST, a second storage capacitor electrode SG2 in contactwith the driving TFT DT, a storage capacitor STG formed by a firststorage capacitor electrode SG1 and the second storage capacitorelectrode SG2 superposed thereon, and an organic light-emitting diodeOLED connected to the driving TFT DT through the second storagecapacitor electrode SG2. The storage capacitor STG and the organiclight-emitting diode OLED are formed in the emission area AA and theTFTs ST and DT or interconnection lines SL, DL and VDD are formed in thenon-emission area NA.

Scan lines SL and data lines DL are formed on the substrate SUB in amatrix form so as to define pixels. The switching TFT ST is formed at anintersection of a scan line SL and a data line DL and serves to select apixel. The switching TFT ST includes a switching gate electrode SG, achannel layer SA, a switching source electrode SS and a switching drainelectrode SD. The switching gate electrode SG is connected to the scanline SL and the switching source electrode SS is branched from the dataline DL.

The driving TFT DT includes a driving gate electrode DG, a channel layerDA, a driving source electrode DS and a driving drain electrode DD. Thedriving gate electrode DG is connected to the switching drain electrodeSD and the driving source electrode DS is branched from the drivingcurrent line VDD.

A passivation layer IN2 is formed to cover the source electrodes SS andDS and the drain electrodes SD and DD of the TFTs ST and DT whileexposing part of the driving drain electrode DD. The second storagecapacitor electrode SG2 is formed on the passivation layer IN2 so as tocome into contact with part of the driving drain electrode DD. Here, thesecond storage capacitor electrode SG2 is superposed on the firststorage capacitor electrode SG1, which is formed when the sourceelectrodes SS and DS and the drain electrodes SD and DD of the TFTs STand DT are formed, having the passivation layer IN2 interposedtherebetween so as to form the storage capacitor STG.

Since the storage capacitor STG is formed in such a manner that thesecond storage capacitor electrode SG2 formed of a transparentconductive material is superposed on the first storage capacitorelectrode SG1 formed of a transparent conductive material, the storagecapacitor STG can have a large area without reducing the aperture ratioin the emission area AA. Accordingly, the organic light-emitting diodedisplay according to the first embodiment of the present invention cansecure the storage capacitor STG having sufficient capacity.

Color filters CF may be formed on the second storage capacitor electrodeSG2 in the emission area AA such that the color filters CF respectivelycorrespond to pixel regions. Here, red, green and blue color filters CFmay be sequentially disposed and the color filters CF may furtherinclude a white color filter CF. Red and/or green color filters CF maybe extended and formed on the portion in which the TFTs ST and DT areformed in the pixel region so as to cover the TFTs ST and DT.

An overcoat layer OC, which exposes part of the second storage capacitorelectrode SG2, is formed on the overall surface of the substrate SUB onwhich the color filters CF are formed. The overcoat layer OC is coatedon the overall surface of the substrate SUB in order to planarize thesurface of the substrate SUB on which the color filters CF are formed.

An anode ANO is formed on the overcoat layer OC to come into contactwith the second storage capacitor electrode SG2. The anode ANO iselectrically connected to the drain electrode DD of the driving TFTthrough the second storage capacitor electrode SG2.

A bank BN, which exposes part of the anode ANO, is formed on the anodeANO. An organic emission layer OLE is formed on part of the bank BN andthe exposed portion of the anode ANO, and a cathode CAT is formed on theorganic emission layer OLE so as to cover the organic emission layerOLE. In this manner, an organic light-emitting diode OLED including theanode ANO, the organic emission layer OLE and the cathode CAT iscompleted.

A description will be given of a process of manufacturing the organiclight-emitting diode display according to the first embodiment of thepresent invention with reference to FIGS. 7A to 7J. Various features ofthe organic light-emitting diode display according to the firstembodiment of the present invention are described in more detail throughthe manufacturing process. FIGS. 7A to 7J are cross-sectional viewsillustrating a method for manufacturing the organic light-emitting diodedisplay according to the first embodiment of the present invention.

Referring to FIG. 7A, an opaque light shielding material is coated onthe overall surface of the substrate SUB and patterned through a firstmask process to form a light shielding layer LS. It is desirable to formthe light shielding layer LS such that semiconductor layers,particularly, channel regions of the TFTs, which will be formed later,are disposed on the light shielding layer LS. The light shielding layerLS serves to protect oxide semiconductor elements from external light.An insulating material is coated on the overall surface of the substrateSUB on which the light shielding layer LS is formed so as to form abuffer layer BF.

Referring to FIG. 7B, a semiconductor material is coated on the overallsurface of the substrate SUB on which the buffer layer BF is formed. Thesemiconductor material may include an oxide semiconductor material suchas indium gallium zinc oxide (IGZO). The semiconductor material layer ispatterned through a second mask process to form semiconductor layers SE.

Referring to FIG. 7C, an insulating material and a metal material aresequentially coated on the overall surface of the substrate SUB on whichthe semiconductor layers SE are formed and simultaneously patternedthrough a third mask process to form a gate insulating layer GI and thegate electrodes SG and DG superposed thereon. The gate electrodes SG andDG are preferably formed such that the gate electrodes SG and DG aredisposed on the center regions of the semiconductor layers SE whileexposing both sides of the semiconductor layers SE. The center regionsof the semiconductor layers SE are respectively defined as a channellayer SA of the switching TFT and a channel layer DA of the driving TFT.The exposed portions of the semiconductor layers SE become sourceregions SSA and DSA and drain regions SDA and DDA respectively cominginto contact with the source electrodes and the drain electrodes of theswitching TFT and the driving TFT. When the semiconductor material is anoxide semiconductor material, the source regions SSA and DSA and thedrain regions SDA and DDA may be conductorized through a plasmatreatment process.

Referring to FIG. 7D, an insulating material is coated on the overallsurface of the substrate SUB on which the gate electrodes SG and DG areformed so as to form an interlevel insulating layer IN1. The interlevelinsulating layer IN1 is patterned through a fourth mask process to formcontact holes SSH and DSH for exposing the source regions SSA and DSA ofthe semiconductor layers and contact holes SDH and DDH for exposing thedrain electrodes SDA and DDA of the semiconductor layers. Here, a gatecontact hole GH for exposing part of the gate electrode DG of thedriving TFT is simultaneously formed.

Referring to FIG. 7E, a transparent conductive material and a metalmaterial are sequentially coated on the interlevel insulating layer IN1in which the contact holes are formed. The transparent conductivematerial may be indium tin oxide, indium zinc oxide, indium tin zincoxide or the like. The transparent conductive material layer and themetal material layer are patterned through a fifth mask process to formthe source electrode SS and the drain electrode SD of the switching TFTST and the source electrode DS and the drain electrode DD of the drivingTFT DT. The first storage capacitor electrode SG1 is formed of thetransparent conductive material in the emission area AA. Here, the drainelectrode SD of the switching TFT is connected to the gate electrode DGof the driving TFT.

The fifth mask process is performed using a half-tone mask. By using thehalf-tone mask, the source electrode SS and the drain electrode SD ofthe switching TFT ST and the source electrode DS and the drain electrodeDD of the driving TFT DT are formed of a double layer including thetransparent conductor layer ITO and the metal material ME, and the firststorage capacitor electrode SG1 is formed of a single layer includingonly the transparent conductive layer ITO. While the source electrodesSS and DS and the drain electrodes SD and DD of the TFTs ST and DT maybe formed of a single layer including only the transparent conductivematerial ITO, it is desirable that the source electrodes SS and DS andthe drain electrodes SD and DD be formed of a double layer including thelaminated transparent conductive material ITO and metal material ME,considering that the transparent conductive material ITO has high sheetresistance.

Referring to FIG. 7F, an insulating material is coated on the overallsurface of the substrate SUB on which the TFTs ST and DT are formed soas to form a passivation layer IN2. The passivation layer IN2 ispatterned through a sixth mask process to form a storage capacitorcontact hole SGH.

Referring to FIG. 7G, a transparent conductive material is coated on theoverall surface of the substrate SUB on which the storage capacitorcontact hole SGH is formed and patterned through a seventh mask processto form the second storage capacitor electrode SG2. It is desirable thatthe second storage capacitor electrode SG2 be formed to be superposed onthe first storage capacitor electrode SG1. The second storage capacitorelectrode SG2 comes into contact with the drain electrode DD of thedriving TFT DT via the storage capacitor contact hole SGH.

Here, the second storage capacitor electrode SG2 is formed on the firststorage capacitor electrode SG1 having the passivation layer IN2interposed therebetween in the emission area AA so as to form thestorage capacitor STG. Accordingly, the first and second storagecapacitor electrodes SG1 and SG2 can be formed in the entire emissionarea AA without decreasing the aperture ratio of the organiclight-emitting diode display according to the first embodiment of thepresent invention since the first and second storage capacitorelectrodes SG1 and SG2 are formed of the transparent conductivematerial. Therefore, the organic light-emitting diode display accordingto the first embodiment of the present invention can secure the storagecapacitor STG having sufficient capacity since the storage capacitorhaving a wide area can be formed.

Referring to FIG. 7H, red, green and blue pigments are coated on theoverall surface of the substrate SUB on which the second storagecapacitor electrode SG2 is formed and sequentially patterned througheighth, ninth and tenth mask processes, respectively, to sequentiallyform red, green and blue color filters CF. The red, green and blue colorfilters CF are selectively formed in pixel regions expressing red, greenand blue. Here, the red and/or green color filters may be extended andformed to cover the TFTs ST and DT in the pixel regions.

Referring to FIG. 7I, an insulating material is coated on the overallsurface of the substrate SUB on which the color filters CF are formed soas to form an overcoat layer OC. The overcoat layer OC is patternedthrough an eleventh mask process to form a pixel contact hole PH.

Referring to FIG. 7J, a transparent conductive material is coated on theoverall surface of the substrate SUB on which the pixel contact hole PHis formed and patterned through a twelfth mask process to form the anodeANO. The anode ANO comes into contact with the second storage capacitorelectrode SG2 via the pixel contact hole PH. In addition, the anode ANOis electrically connected to the drain electrode DD of the driving TFTthrough the second storage capacitor electrode SG2.

The organic light-emitting diode display according to the firstembodiment of the present invention can secure the storage capacitor STGhaving sufficient capacity since the first and second storage capacitorelectrodes SG1 and SG2 can be formed to have a wide area in the emissionarea AA without decreasing the aperture ratio. Consequently, the organiclight-emitting diode display can sustain pixel data until the nextperiod using charges of the storage capacitor STG when the driving TFTDT is in an off state.

Second Embodiment

A description will be given of an organic light-emitting diode displayaccording to a second embodiment of the present invention with referenceto FIGS. 8 and 9. FIG. 8 is a plan view illustrating a structure of anorganic light-emitting diode display according to the second embodimentof the present invention and FIG. 9 is a cross-sectional viewillustrating the structure of the organic light-emitting diode displayaccording to the second embodiment of the present invention, taken alongline III-III′ of FIG. 8.

Referring to FIGS. 8 and 9, the organic light-emitting diode displayaccording to the second embodiment of the present invention includes asubstrate SUB in which an emission area AA and a non-emission area NAare defined, a switching TFT ST, a first storage capacitor electrode SG1connected to the switching TFT ST, a driving TFT DT connected to theswitching TFT ST, a second storage capacitor electrode SG2 connected tothe driving TFT DT, a storage capacitor STG formed by the first storagecapacitor electrode SG1 and the second storage capacitor electrode SG2superposed thereon, and an organic light-emitting diode OLED connectedto the driving TFT DT. The storage capacitor STG and the organiclight-emitting diode OLED are formed in the emission area AA, and theTFTs ST and DT or interconnection lines SL, DL VDD are formed in thenon-emission area NA.

Scan lines SL and data lines DL are formed on the substrate SUB in amatrix form so as to define pixels. The switching TFT ST is formed at anintersection of a scan line SL and a data line DL and serves to select apixel. The switching TFT ST includes a switching gate electrode SG, achannel layer SA, a switching source electrode SS and a switching drainelectrode SD. The switching gate electrode SG is branched from the scanline SL and the switching source electrode SS is branched from the dataline DL.

The driving TFT DT includes a driving gate electrode DG, a channel layerDA, a driving source electrode DS and a driving drain electrode DD. Thedriving gate electrode DG is connected to the switching drain electrodeSD and the driving source electrode DS is branched from the drivingcurrent line VDD.

A first transparent conductive layer ITO1, a light shielding layer SLSand DLS and a buffer layer BF, which have an area wider than asemiconductor layers SE of the TFTs ST and DT, are sequentially formedunder the switching TFT ST and the driving TFT DT. The light shieldinglayer SLS and DLS serves to protect oxide semiconductor elements fromexternal light.

More specifically, the emission area AA and the non-emission area NA aredefined on the substrate SUB. The first transparent conductive layerITO1, the light shielding layer SLS and DLS and the buffer layer BF aresequentially formed on the non-emission area NA. The semiconductor layerSE is formed on the light shielding layer SLS and DLS and the bufferlayer BF such that the semiconductor layer SE has an area narrower thanthe light-shielding layer SLS and DLS and the buffer layer BF. A gateinsulating layer GI and the gate electrodes SG and DG are sequentiallyformed on the semiconductor layer SE such that the gate insulating layerGI and the gate electrodes SG and DG are disposed on the center regionsof the semiconductor layer SE. An interlevel insulating layer IN1 isformed on the overall surface of the substrate SUB to cover both sidesof the semiconductor layer SE and the gate electrodes SG and DG. Thesource electrodes SS and DS and the drain electrodes SD and DD areformed on the interlevel insulating layer IN1 and respectively come intocontact with both sides of the semiconductor layer SE through contactholes SSH, DSH, SDH and DDH which penetrate the interlevel insulatinglayer IN1. The source electrodes SS and DS and the drain electrodes SDand DD may be formed of a double layer including a second transparentconductive layer ITO2 and a metal layer ME formed thereon. Here, thedrain electrode SD of the switching TFT ST and the gate electrode DG ofthe driving TFT DT are connected through a gate contact hole GH. In thismanner, the switching TFT ST and the driving TFT DT are completed.

The second transparent conductive layer ITO2, which forms the drainelectrode DD of the driving TFT DT, is extended to the emission area AA.The second transparent conductive layer ITO2 extended to the emissionarea AA serves as the second storage capacitor electrode SG2. The secondstorage capacitor electrode SG2 is superposed on the first storagecapacitor electrode SG1, which is formed when the first transparentconductive layer ITO1 disposed under the light shielding layer isformed, having the interlevel insulating layer IN1 interposedtherebetween so as to form the storage capacitor STG. The first storagecapacitor SG1 is connected to the drain electrode SD of the switchingTFT ST through a storage capacitor contact hole SGH.

Since the storage capacitor STG is formed in such a manner that thesecond storage capacitor electrode SG2 formed of a transparentconductive material is superposed on the first storage capacitorelectrode SG1 formed of a transparent conductive material, the storagecapacitor STG can be formed to have a large area without reducing theaperture ratio in the emission area AA. Accordingly, the organiclight-emitting diode display according to the second embodiment of thepresent invention can secure a storage capacitor STG having sufficientcapacity.

A passivation layer IN2 is formed on the overall surface of thesubstrate SUB on which the source electrodes SS and DS and the drainelectrodes SD and DD of the TFTs ST and DT and the second storagecapacitor electrode SG2 are formed. Part of the drain electrode DD ofthe driving TFT DT is exposed through a pixel contact hole PH formed inthe passivation layer IN2.

Color filters CF may be formed on the second storage capacitor electrodeSG2 in the emission area AA such that the color filters CF respectivelycorrespond to pixel regions. Here, red, green and blue color filters CFmay be sequentially arranged and the color filters CF may furtherinclude a white color filter CF. Here, red and/or green color filters CFmay be extended to and formed on the region in which the TFTs ST and DTare formed in the pixel region so as to cover the TFTs ST and DT, whichis not shown.

An overcoat layer OC, which exposes the pixel contract hole PH, isformed on the overall surface of the substrate SUB on which the colorfilters CF are formed. The overcoat layer OC is coated on the overallsurface of the substrate SUB in order to planarize the surface of thesubstrate SUB on which the color filters CF are formed.

An anode ANO is formed on the overcoat layer OC to come into contactwith the drain electrode DD of the driving TFT DT through the pixelcontact hole PH. Accordingly, the anode ANO, the drain electrode DD ofthe driving TFT DT and the second storage capacitor electrode SG2 areelectrically connected.

A bank BN which exposes part of the anode ANO is formed on the anodeANO. An organic emission layer OLE is formed on the exposed portion ofthe anode ANO, and a cathode CAT is formed on the organic emission layerOLE to cover the organic emission layer OLE. In this manner, the organiclight-emitting diode OLED including the anode ANO, the organic emissionlayer OLE and the cathode CAT is completed.

A description will be given of a process of manufacturing the organiclight-emitting diode display according to the second embodiment of thepresent invention with reference to FIGS. 10A to 10J. Various featuresof the organic light-emitting diode display according to the secondembodiment of the present invention are described in more detail throughthe manufacturing process. FIGS. 10A to 10J are cross-sectional viewsillustrating a method for manufacturing the organic light-emitting diodedisplay according to the second embodiment of the present invention.

Referring to FIGS. 10A and 10B, a first transparent conductive material,an opaque light shielding material, an insulating material and asemiconductor material are sequentially coated on the overall surface ofthe substrate SUB. The transparent conductive material may be indium tinoxide, indium zinc oxide, indium tin zinc oxide or the like. Thesemiconductor material may include an oxide containing oxygen and atleast one of indium, gallium, zinc and tin, for example, an oxidesemiconductor material such as indium gallium zinc oxide (IGZO). Thefirst transparent conductive material layer, the opaque light shieldingmaterial layer, the insulating material layer and the semiconductormaterial layer are patterned through a first mask process to form thefirst transparent conductive layer ITO1, the light shielding layer SLS,DLS and LS, the buffer layer BF and the semiconductor layer SE. Thefirst conductive layer ITO1 formed on the emission area AA serves as thefirst storage capacitor electrode SG1.

More specifically, the first transparent conductive material, the lightshielding material, the insulating material, the semiconductor materialand a photoresist are sequentially coated on the substrate SUB. Ahalf-tone mask for patterning the first transparent conductive materiallayer, the light-shielding material layer, the insulating materiallayer, the semiconductor material layer and the photoresist through thefirst mask is prepared. The half-tone mask includes a full-tone area forshielding light projected thereto, a half-tone area for transmittingpart of light projected thereto and shielding part thereof, and an areafor completely transmitting light projected thereto. Light isselectively projected through the prepared half-tone mask. Here, thephotoresist may be of positive type or negative type. A case in which apositive type photoresist is used is will now be described.

When the photoresist exposed through the half-tone mask is developed,photoresist patterns PR1 corresponding to the full-tone area and thehalf-tone area of the half-tone mask remain. Here, the photoresistpattern PR1 corresponding to the full-tone area is thicker than thephotoresist pattern PR1 corresponding to the half-tone area. The firsttransparent conductive material layer, the light shielding materiallayer, the insulating material layer and the semiconductor materiallayer are primarily patterned using the remaining photoresist patternsPR1. The light shielding layer SLS, DSL and LS and the buffer layer BFare formed according to the primary patterning. The first transparentconductive layer ITO1 remains beneath the light shielding layer SLS, DLSand LS. Here, the first transparent conductive layer remaining on theemission area AA serves as the first storage capacitor electrode SG1.Semiconductor layer patterns SM formed through primary patterning remainon the buffer layer BF (FIG. 10A).

Subsequently, an asking process for removing the photoresist patternsPR1 by a predetermined thickness is performed such that only thephotoresist pattern PR1 corresponding to the full-tone area remains. Thesemiconductor patterns SM are secondarily patterned using the remainingphotoresist pattern PR1 so as to form semiconductor layers SE. Here, thesemiconductor pattern SM on the emission area AA is removed.Subsequently, the remaining photoresist pattern PR1 is removed through astripping process (FIG. 10B).

The light shielding layer SLS and DLS has an area wider than thesemiconductor layers SE according to patterning using the half-tonemask. The light shielding layer SLS and DLS serves to protect oxidesemiconductor elements from external light. Accordingly, it is desirablethat the light shielding layer SLS and DLS be superposed on thesemiconductor layers SE while having a wider area than the semiconductorlayers SE in order to effectively protect the semiconductor layers SE.

Referring to FIGS. 10C and 10D, an insulating material and a metalmaterial are sequentially coated on the overall surface of the substrateSUB on which the semiconductor layers SE are formed and simultaneouslypatterned through a second mask process to form the gate insulatinglayer GI and the gate electrodes SG and DG superposed thereon. The gateelectrodes SG and DG are formed such that the gate electrodes SG and DGare respectively disposed on the center regions of the semiconductorlayers SE while exposing both sides of the semiconductor layers SE. Thecenter regions of the semiconductor layer SE are respectively defined asa channel layer SA of the switching TFT and a channel layer DA of thedriving TFT. The exposed portions of the semiconductor layers SE becomesource regions SSA and DSA and drain regions SDA and DDA respectivelycoming into contact with the source electrodes and the drain electrodesof the switching TFT and the driving TFT. When the semiconductormaterial is an oxide semiconductor material, the source regions SSA andDSA and the drain regions SDA and DDA may be conductorized through aplasma treatment process.

The second mask process is performed using a half-tone mask. Aninsulating layer, a metal material and a photoresist are sequentiallycoated on the overall surface of the substrate SUB on which thesemiconductor layers SE are formed. Then, light is selectively projectedthrough the half-tone mask. When the photoresist exposed through thehalf-tone mask is developed, photoresist patterns PR2 corresponding tothe full-tone area and the half-tone area of the half-tone mask remain.Here, the photoresist pattern PR2 corresponding to the full-tone area isthicker than the photoresist pattern PR2 corresponding to the half-tonearea. The insulating material layer and the metal material layer areprimarily patterned using the remaining photoresist patterns PR2.According to primary patterning, an insulating material pattern IM and ametal pattern GM are formed. Here, the light shielding layer LS and thebuffer layer BF formed on the first storage capacitor electrode SG1 areremoved (FIG. 10C).

Subsequently, an asking process for removing the photoresist patternsPR2 by a predetermined thickness is performed such that only thephotoresist pattern PR2 corresponding to the full-tone area remains. Theinsulating material pattern IM and the metal pattern GM are secondarilypatterned using the remaining photoresist pattern PR2 so as to form thegate insulating layer GI and the gate electrodes SG and DG superposedthereon. Subsequently, the remaining photoresist pattern PR2 is removedthrough a stripping process (FIG. 10D).

Referring to FIG. 10E, an insulating material is coated on the overallsurface of the substrate SUB on which the gate electrodes SG and DG areformed so as to form an interlevel insulating layer IN1. The interlevelinsulating layer IN1 is patterned through a third mask process to formcontact holes SSH and DSH for exposing the source regions SSA and DSA ofthe semiconductor layers and contact holes SDH and DDH for exposing thedrain electrodes SDA and DDA of the semiconductor layers. Here, a gatecontact hole GH for exposing part of the gate electrode DG of thedriving TFT is simultaneously formed. Furthermore, the storage capacitorcontact hole SGH (refer to FIG. 8) for exposing part of the firststorage capacitor electrode SG1 is formed, which is not shown.

Referring to FIG. 10F, a second transparent conductive material and ametal material are sequentially coated on the interlevel insulatinglayer IN1 in which the contact holes are formed. The second transparentconductive material layer and the metal layer are patterned through afourth mask process to form the source electrode SS and the drainelectrode SD of the switching TFT ST and the source electrode DS and thedrain electrode DD of the driving TFT DT. The second storage capacitorelectrode SG2 is formed of the second transparent conductive material inthe emission area AA. Here, the drain electrode DD of the driving TFT DTand the second storage capacitor electrode SG2, which are formed of thesecond transparent conductive material, are connected as one body. It isdesirable that the second storage capacitor electrode SG2 is superposedon the first storage capacitor electrode SG1.

The drain electrode SD of the switching TFT ST is connected to the gateelectrode DG of the driving TFT. In addition, the drain electrode SD ofthe switching TFT ST is connected to the first storage capacitorelectrode SG1 through the storage capacitor contact hole SGH (FIG. 8).

The second storage capacitor electrode SG2 is formed on the firststorage capacitor electrode SG1 having the interlevel insulating layerIN1 interposed therebetween in the emission area AA so as to form thestorage capacitor STG. Accordingly, the first and second storagecapacitor electrodes SG1 and SG2 can be formed in the entire emissionarea AA without decreasing the aperture ratio of the organiclight-emitting diode display according to the second embodiment of thepresent invention since the first and second storage capacitorelectrodes SG1 and SG2 are formed of the transparent conductivematerial. Therefore, the organic light-emitting diode display accordingto the second embodiment of the present invention can secure the storagecapacitor STG having sufficient capacity since the storage capacitor STGhaving a wide area can be formed.

The fourth mask process is performed using a half-tone mask. By usingthe half-tone mask, the source electrode SS and the drain electrode SDof the switching TFT ST and the source electrode DS and the drainelectrode DD of the driving TFT DT are formed of a double layerincluding the second transparent conductor layer ITO2 and the metalmaterial ME, and the second storage capacitor electrode SG2 is formed ofa single layer including only the second transparent conductive layer1102. While the source electrodes SS and DS and the drain electrodes SDand DD of the TFTs ST and DT may be formed of a single layer includingonly the second transparent conductive material ITO2, it is desirablethat the source electrodes SS and DS and the drain electrodes SD and DDbe formed of a double layer including the second transparent conductivematerial ITO2 and metal material ME formed thereon, considering that thesecond transparent conductive material ITO2 has high sheet resistance.

Referring to FIG. 10G, an insulating material is coated on the overallsurface of the substrate SUB on which the TFTs ST and DT are formed soas to form a passivation layer IN2. Subsequently, the passivation layerIN2 is patterned through a fifth mask process to form the pixel contacthole PH.

Referring to FIG. 10H, red, green and blue pigments are coated on theoverall surface of the substrate SUB on which the second storagecapacitor electrode SG2 is formed and sequentially patterned throughsixth, seventh and eighth mask processes, respectively, to sequentiallyform red, green and blue color filters CF. The red, green and blue colorfilters CF are selectively formed in pixel regions expressing red, greenand blue.

Referring to FIG. 10I, a photosensitive insulating material is coated onthe overall surface of the substrate SUB on which the color filters CFare formed so as to form an overcoat layer OC. The overcoat layer OC ispatterned through a ninth mask process to form the pixel contact holePH.

Referring to FIG. 10J, a third transparent conductive material is coatedon the overall surface of the substrate SUB on which the pixel contracthole PH and the overcoat layer OC are formed and patterned through atenth mask process to form the anode ANO. The anode ANO comes intocontact with the drain electrode DD of the driving TFT DT through thepixel contact hole PH. Accordingly, the anode ANO, the drain electrodeDD of the driving thin film transistor DT and the second storagecapacitor electrode SG2 are electrically connected.

The organic light-emitting diode display according to the secondembodiment of the present invention can secure the storage capacitor STGhaving sufficient capacity since the first and second storage capacitorelectrodes SG1 and SG2 can be formed to have a wide area in the emissionarea AA without decreasing the aperture ratio. Consequently, the organiclight-emitting diode display can sustain pixel data until the nextperiod using charges of the sufficient storage capacitor STG when thedriving TFT DT is in an off state.

Furthermore, the second embodiment of the present invention can reducetwo mask processes before the formation of the anode ANO, compared tothe first embodiment. Accordingly, a plurality of processing steps, suchas exposure, development, etching and cleaning, included in a maskprocess can be reduced, and thus the manufacturing process can besimplified and the manufacturing cost and time can be decreased.Furthermore, a defect generation rate can be reduced, improvingproduction yield.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the scope of the principles of thisdisclosure. More particularly, various variations and modifications arepossible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

What is claimed is:
 1. An organic light-emitting diode display,comprising: a substrate in which an emission area and a non-emissionarea are defined; a first transparent conductive layer, a lightshielding layer, a buffer layer and a semiconductor layer sequentiallylaminated on the non-emission area; a gate electrode superposed on acenter region of the semiconductor layer, and having a gate insulatinglayer interposed therebetween; a drain electrode coming into contactwith one side of the semiconductor layer, having an interlevelinsulating layer covering the gate electrode interposed therebetween,and formed of a second transparent conductive layer and a metal layerlaminated thereon; a first storage capacitor electrode disposed underthe interlevel insulating layer in the emission area and formed of thefirst transparent conductive layer; and a second storage capacitorelectrode superposed on the first storage capacitor electrode in theemission area, having the interlevel insulating layer interposedtherebetween, and formed of the second transparent conductive layer,wherein the buffer layer and the semiconductor layer are patterned to bedisposed on the light shielding layer and not to be disposed on thefirst storage capacitor electrode.
 2. The organic light-emitting diodedisplay of claim 1, further comprising: a source electrode coming intocontact with the other side of the semiconductor layer, having theinterlevel insulating layer interposed therebetween, formed of thesecond transparent conductive layer and the metal layer laminatedthereon, and disposed at a predetermined distance from the drainelectrode; an overcoat layer disposed on the source electrode, the drainelectrode and the second storage capacitor electrode; and an anodedisposed on the overcoat layer and coming into contact with part of thedrain electrode.
 3. The organic light-emitting diode display of claim 1,wherein the first transparent conductive layer and the first storagecapacitor electrode are formed of a same material and disposed at a samelevel.
 4. The organic light-emitting diode display of claim 1, whereinthe second storage capacitor electrode is disposed in such a manner thatthe second transparent conductive layer of the drain electrode isextended to the emission area.
 5. A method for manufacturing an organiclight-emitting diode display, the method comprising: forming a firsttransparent conductive layer, a light shielding layer, a buffer layerand a semiconductor layer on a non-emission area of a substrate using afirst transparent conductive material, a light shielding material, aninsulating material and a semiconductor material, respectively, andforming a first storage capacitor electrode on an emission area of thesubstrate using the first transparent conductive material; forming agate electrode superposed on a center region of the semiconductor layerand having a gate insulating layer interposed therebetween; forming aninterlevel insulating layer on the overall surface of the substrate onwhich the gate electrode is formed; and forming, on the interlevelinsulating layer, a drain electrode coming into contact with one side ofthe semiconductor layer and formed of a second transparent conductivelayer and a metal layer laminated thereon, a source electrode cominginto contact with the other side of the semiconductor layer and formedof the second transparent conductive layer and the metal layer laminatedthereon, and a second storage capacitor electrode superposed on thefirst storage capacitor electrode and formed of the second transparentconductive layer of the drain electrode, extended to the emission area,wherein the buffer layer and the semiconductor layer are patterned to bedisposed on the light shielding layer and not to be disposed on thefirst storage capacitor electrode.
 6. The method of claim 5, furthercomprising: forming an overcoat layer on the overall surface of thesubstrate on which the source electrode, the drain electrode and thesecond storage capacitor electrode are formed; and forming an anodecoming into contact with part of the drain electrode on the overcoatlayer.
 7. The organic light-emitting diode display of claim 1, whereinthe drain electrode and the second storage capacitor electrode share onelayer, and wherein the number of layers constituting the drain electrodeand the second storage capacitor electrode is different from each other.